[PATCH AUTOSEL 6.14 550/642] net: flush_backlog() small changes

Sasha Levin
2025-05-05T22:36:28Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit cbe08724c18078564abefbf6591078a7c98e5e0f ]

Add READ_ONCE() around reads of skb->dev->reg_state, because
this field can be changed from other threads/cpus.

Instead of calling dev_kfree_skb_irq() and kfree_skb()
while interrupts are masked and locks held,
use a temporary list and use __skb_queue_purge_reason()

Use SKB_DROP_REASON_DEV_READY drop reason to better
describe why these skbs are dropped.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Link: https://patch.msgid.link/20250204144825.316785-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/dev.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 2f7f5fd9ffec7..77306b522966c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6187,16 +6187,18 @@ EXPORT_SYMBOL(netif_receive_skb_list);
static void flush_backlog(struct work_struct *work)
{
struct sk_buff *skb, *tmp;
+ struct sk_buff_head list;
struct softnet_data *sd;

+ __skb_queue_head_init(&list);
local_bh_disable();
sd = this_cpu_ptr(&softnet_data);

backlog_lock_irq_disable(sd);
skb_queue_walk_safe(&sd->input_pkt_queue, skb, tmp) {
- if (skb->dev->reg_state == NETREG_UNREGISTERING) {
+ if (READ_ONCE(skb->dev->reg_state) == NETREG_UNREGISTERING) {
__skb_unlink(skb, &sd->input_pkt_queue);
- dev_kfree_skb_irq(skb);
+ __skb_queue_tail(&list, skb);
rps_input_queue_head_incr(sd);
}
}
@@ -6204,14 +6206,16 @@ static void flush_backlog(struct work_struct *work)

local_lock_nested_bh(&softnet_data.process_queue_bh_lock);
skb_queue_walk_safe(&sd->process_queue, skb, tmp) {
- if (skb->dev->reg_state == NETREG_UNREGISTERING) {
+ if (READ_ONCE(skb->dev->reg_state) == NETREG_UNREGISTERING) {
__skb_unlink(skb, &sd->process_queue);
- kfree_skb(skb);
+ __skb_queue_tail(&list, skb);
rps_input_queue_head_incr(sd);
}
}
local_unlock_nested_bh(&softnet_data.process_queue_bh_lock);
local_bh_enable();
+
+ __skb_queue_purge_reason(&list, SKB_DROP_REASON_DEV_READY);
}

static bool flush_required(int cpu)
--
2.39.5